This invention relates to hydraulic brake actuating and locking devices, and while the invention is subject to a wide range of applications, it will be particularly described as a brake cylinder having a hydraulically operated lock for its push rod.
The present invention is particularly useful in a hydraulic braking system such as is disclosed, for example, in the Engle U.S. Pat. No. 3,508,794, issued Apr. 27, 1970, and assigned to the same assignee as is the present invention. This patent is incorporated by reference in the present application. According to the patent, braking of a vehicle is selectively rendered effective by fluid braking pressure applied to brake cylinders either by conventional service brake control or by a fluid operated hand brake control system for parking purposes, and the like.
Because of its being desirable to maintain parking brakes applied for long periods of time when a car is unattended, a system is provided according to the above patent for mechanically locking braking push rods in their extended braking positions relative to their associated brake cylinder. This locking mechanism is selectively rendered effective or ineffective by hydraulic hand brake control. Improvements in this locking mechanism are disclosed in the Engle U.S. Pat. No. 3,586,138, issued June 22, 1971, also assigned to the same assignee as the present invention and hereby incorporated by reference in the present application.
In both of the above patents, the mechanical locking is accomplished by clamping the outer periphery of the push rods to prevent movement relative tto the associated brake cylinder. Repeated use of this locking device, together with mechanical strains such as the coupling of other cars to a car having its brakes locked can wear the periphery of the push rod to an extent to require maintenance in order to prevent damage to seals and/or push rod bearings.
An object of the present invention is to provide a hydraulic brake actuating and locking device which substantially obviates one or more of the limitations and disadvantages of the described prior arrangements.
Another object of the present invention is to provide a hydraulic brake actuating and locking device obviating the necessity for clamping the outer periphery of a push rod in order to provide axial locking of the push rod relative to the brake cylinder.
Other objects, purposes, and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.